Yeah, well, that is a lie.
On XSX, as in PS5, the games that are going to be "boosted" are the ones with uncapped framerates or dynamic resolution, the games that do not meet this criteria, will run as they did this gen. Again, both in XSX and PS5.
But keep on keeping on, all that bullshit is not going to spill by itself.
Oh, and before you come at me with the PR stuff Microsoft said about "no boost mode, no downclocking, every game will take full advantage of the Series X hardware", here, take a look at the article and read carefully the phrase "This means that all titles run at the peak performance that they were originally designed for". So, again, if a game was designed at a capped 30fps and 1080p resolution, that's how it's going to run on Series X. Same as PS5, of course, Sony has absolutely no advantages on BC, Xbox is still doing a better job overall, but don't lie.
https://news.xbox.com/en-us/2020/05/28/xbox-series-x-next-generation-backward-compatibility/